1. Field of the Invention
This invention relates to rocket motors employing solid propellant grains, and is particularly directed to a hybrid rocket motor of this type incorporating improved means for injection of oxidizer into the propellant grain during combustion thereof. A hybrid rocket motor is a rocket motor that uses a solid fuel and a liquid oxidizer.
2. Description of the Prior Art
In prior art rocket motors utilizing solid fuel propellant grains, oxidizer such as liquid oxygen is fed in the head end of the rocket motor into a port or cavity in the solid fuel grain for combustion thereof. Thus, a conventional flat or curved shower head-type injector is typically disposed at the head end of the motor, and discharges a spray of liquid droplets into the central cavity of the solid propellant. A field of near zero relative combustion gas to oxidizer droplet velocity occurs near the head end of the rocket motor, with large amounts of liquid droplets, which can produce unstable burning of solid propellant. Further, when employing such shower head-type injectors, which are of relatively large diameter, as the propellant grain burns away, it exposes areas at the head end of the rocket motor which are not part of the injector. That part which is thus exposed as the solid propellant is subject to being burned away, since it does not have oxidizer flowing through it sufficient to cool it. Thus, prior art rocket motors suffer from the disadvantages of non-uniform injection of oxidizer and non-uniform combustion of solid propellant along the length of the propellant grain, and can result in combustion instability, and insufficient cooling of the oxidizer injector.